The invention relates to a process for the selective removal of inorganic and/or organic sulfur compounds, such as H.sub.2 S, COS, CS.sub.2, thiols, and the like, from gases which contain, in addition, at least one of the components H.sub.2, N.sub.2, Ar, CO.sub.2, CO, and aliphatic hydrocarbons by scrubbing with a physical scrubbing agent, i.e., a scrubbing agent which does not depend on a chemical reaction with the absorbed compound.
For the selective removal of sulfur compounds from gases which, besides H.sub.2 S, can contain other inorganic and organic sulfur compounds, such as, for example, COS, CS.sub.2, thiols, etc., physical, as well as chemical, scrubbing agents have been used for many years.
A detailed discussion of various scrubbing processes can be found, for example, in A. L. Kohl, F. C. Riesenfeld: "Gas Purification," 4th ed , Gulf Publishing Co., Houston, Tex. (1985); S. A. Newman (Editor): "Acid and Sour Gas Treating Processes," Gulf Publishing Co., Houston, Texas (1985); as well as in R. N. Maddox: "Gas Conditioning and Processing," Vol. IV, Campbell Petroleum Series, Norman, Okla. (1982).
With physical scrubbing agents, because of the different specific physical intermolecular interactions between individual functional groups of the scrubbing agent or of the scrubbing agent molecule in its structural composition as a whole, individual gas components are preferably absorbed from gas mixtures. The specific solubility characteristics are also affected by different arrangements of the same functional groups in the scrubbing agent molecule, since the different locations of the functional groups cause different electron configurations. In these processes, the most important process steps, i.e., absorption of the components to be scrubbed out and regeneration of the scrubbing agent, are determined by the specific physical solubility characteristics of the individual gas components. As physical scrubbing agents in known processes, there can be mentioned, for example, methanol, N-methylpyrrolidone (NMP) and polyethylene glycol dialkyl ether (PGE), among others.
Acid gas removal by chemical scrubbing agents is based on a completely different principle which takes advantage of the fact that specific chemical or electrolytic reactions take place between individual solvent components and the acid gas components to be scrubbed out*-*. In chemical scrubbing processes for the selective removal of sulfur, there have been used preferably tertiary amines, e.g., methyldiethanolamine (MDEA), in aqueous solutions, with the water content being usually more than 40% by weight. FNT With these processes, besides the physical, chemical and electrolytic balances, the kinetics and the transport processes are thus the dominant valves.
It is also known to remove sulfur components by both physically and chemically active scrubbing agents, so-called hybrid scrubbing agents. This type of scrubbing agent uses the advantages of the chemical as well as those of the physical scrubbing agents. Thus, by the presence of purely physical scrubbing agent components, organic sulfur compounds can also be scrubbed out, which with a purely chemical scrubbing agent is possible only in a limited way.
To increase the selectivity between CO.sub.2 and H.sub.2 S in these processes, i.a., advantage is taken of the fact that in aqueous solutions, the electrolytic and chemical reactions of CO.sub.2 are partly kinetically hindered and occur at a substantially slower rate than those of H.sub.2 S. But since H.sub.2 S must be scrubbed out to a residual content of a few ppm, normally 20 to 30% of the CO.sub.2 contained in the crude gas is also scrubbed out.
With the known physical scrubbing agents, a substantial disadvantage exists insofar as besides H.sub.2 S and less volatile sulfur components (for example, thiols, CS.sub.2, etc.) there are also scrubbed out a considerable part of the CO.sub.2 as well as higher hydrocarbons. In most cases, it is also necessary to conduct an at least partial separation of these additional components from the sulfur components to obtain a sulfur-rich fraction amenable-to the requisite conversion reactions to elementary sulfur in a relatively problem-free manner. In many cases this not only results in complicating the scrubbing process but also increases the consumption and the investment costs. Corresponding to the vapor pressure of the scrubbing agent, both the scrubbed product gas and the sulfur component fraction contain undesirable scrubbing agent components, which, on the one hand, increase the investment and operation costs of the system and, on the other hand, represent possibly troublesome impurities in the product gas.
The most important disadvantages in chemical scrubbing processes are that the selectivity between H.sub.2 S and CO.sub.2 is small and the energy consumption in the regeneration of the loaded scrubbing agent is relatively high. Further, in chemical scrubbing processes, loading of the scrubbing agent is dependent on the chemical equilibrium. Since the chemical equilibriums are only slightly dependent on pressure, chemical scrubbing processes are preferably used at low pressures.
Conversely, with sulfur-containing synthesis gases at high pressures and with a higher CO.sub.2 content, in which CO.sub.2 can or is to remain in the scrubbed gas and the sulfur components are to be lowered to a few ppm, the use of physical scrubbing agents is significantly more advantageous in comparison with chemical scrubbing agents.